抄録
To perform the vector control, relatively complicated control algorythm is required. The digital sampling control system is apt to be unstable dependent on its sampling period. To equip with many functions under the limitation of lower cost, the longer sampling period is inevitable and the performance of the system becomes less stable. Therefore it is important to evaluate the permissible maximum sampling period of each system.
To evaluate it, software simulation tools such as PSIM and EMTP can be used. However these tools require a long execution time even for the sole model under each circuit condition. Therefore simpler methods are necessary to investigate the stability rapidly for many cases of the circuit conditions.
In this paper, we propose three kinds of stability judging methods using root loci in a z-plane. The first metod is the most practical one based on a simple approximated model. The second and third methods are based on detailed models each having continuously rotating axis and stepwise rotating axis of the motor coordinates.
To evaluate the proposed analytical methods, these results are compared with those obtained from detailed simulation taking PWM control into account.
