双三相分段供电永磁直线同步电机电感分析与不平衡抑制

Inductance Analysis and Imbalance Suppression of the Sectionally Powered Dual Three-phases Permanent Magnet Linear Synchronous Machine

长初级直线电机通常采用分段供电的方式以降低供电成本和提高功率因数,然而初级侧分段会导致电机中的电感不平衡,从而引发推力波动,致使系统性能下降。针对双三相分段供电永磁直线同步电机的六相不平衡问题进行了研究,分别推导出了直线电机的边端供电段和直线电机中间供电段绕组产生的气隙磁场分布的解析表达式以及对应的自感和互感表达式,并且通过有限元验证了表达式的正确性。分析表明,六相电感不平衡的根源在于相邻未供电段铁芯的磁路与供电段铁芯存在耦合而导致的气隙磁密分布中的脉振分量。为了抑制六相电感的不平衡,在供电段之间加入良导体制成的屏蔽层以阻隔相邻铁芯间的磁路,随着电机速度和运行频率的增加,屏蔽层对六相电感不平衡的抑制作用明显提升。最后,分别对加入屏蔽层的电机加载平衡六相电压和通入平衡六相电流后电机的电流、电压、推力及损耗特性进行研究。结果表明,屏蔽层对六相不平衡电压、六相不平衡电流以及由不平衡电流带来的推力波动具有明显抑制作用,同时对铁耗具有明显降低作用。

In order to obtain high power factor and reduce the cost of the power supply, linear machines with long primary side are usually separated into several sections and only activated the sections covered by the mover. However, the sectional structure leads to the inductance unbalance, which results in the thrust ripple and deteriorates the performance of the linear drive system. In this paper, the unbalance six-phase inductances in sectionally powered dual three-phase permanent magnet linear synchronous machine(PMLSM) is researched. The air-gap flux distribution generated by phase windings is derived and the inductances are also accordingly calculated. The analytical results are validated by finite element method. It is found that the unbalance six-phase inductances are caused by the iron cores in the sections next to the powered section. The flux generated by the windings in the powered section goes through the adjacent iron core and causes the DC component in the flux distribution. To suppress the unbalance in six-phase inductances, shield layers made of conductive material are inserted between the two adjacent sections. With the shield layers between sections, the six-phase inductances become more and more balance as the mover speed and operation frequency goes up. Finally, the current, voltage, force and loss characteristics are researched with balance six-phase voltages, balance six-phase currents. The results show that the shield layers successfully balance the voltages and currents. The force fluctuation which is caused by the unbalance currents is suppressed by the shield layers, the iron loss is also reduced.