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BMEP581020
BMEP581020
变频器按照电机正常运行时的转动方向,缓慢旋转其施加在电枢绕组上的电压矢量。随着同步电机转子的转动和定子磁场的旋转,转子磁极将在某一时刻掠过定子的异性磁极,或者转子磁极加速追上旋转的定子磁极。此时,电机的转子磁极被较强的定子磁极可靠吸引,二者间的角度经过少量有阻尼的震荡后,逐渐趋于一个较小的常量。至此,同步电机进入同步运行状态,整步过程完成。
第四步,变频器按照预先设定的加速度和V/F曲线(即磁通给定),调节输出电压,逐渐加速到给定频率。此时,同步电机的转子角逐渐拉大到某一常值,然后电机转子磁极在定子磁场的吸引下逐渐加速至期望转速,同步电机起动过程完成。
在同步电机的起动整步过程中,定、转子磁势大小的选择和各步骤间的切换是控制的关键问题。如果选择过低的定子磁场,则定子磁极无法在第一次经过转子的异性磁极时,将其可靠吸牢,此后转子经过同性磁极间斥力的反向加速作用,在下一次经过定子磁极时,二者将具有更大的相对速度,定子磁场更加无法有效牵引转子磁极,终将导致起动整步失败。选择过大的定子磁场可能导致同步电机的定子铁心饱和,进一步导致变频器输出过电流,电机起动失败。
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