| 摘要 |
PURPOSE:To change effective input voltage in response to load and operate an induction motor at the maximum efficniency at all times by a method wherein voltage corresponding to load currents and saw tooth waves synchronizing with bus voltage are compared, and thyristors are controlled. CONSTITUTION:Three phase bus bars 10 are connected to an induction meotor 12 through two-way thyristors 11 every each phase. Load currents are detected by means of a current transformer 13, and transmitted to a comparator 15 through an absolute-value circuit 14 while the output of a saw tooth wave generating circuit 16 controlled by means of a phase detecting circuit 20 is also delivered to the comparator 15, comparison output is supplied to a control circuit 17 during the time when a level of the absolute-value circuit 14 is larger than a level of saw tooth waves, the gates of the thristors 11 are controlled and the motor 12 is operated. Thus, since applied voltage is controlled in response to the load currents and the motor can be operated at rated load at all times, necessary input is reduced, and the maximum efficiency can be obtained. |
