| 摘要 |
<P>PROBLEM TO BE SOLVED: To solve the problem of a device for detecting the rotational direction or the r.p.m. of an induction motor under free run state, wherein since a DC current is conventionally applied stepwise, pulse frequency of the ripple components of current and voltage being generated at that time is measured, such characteristics as that frequency is substantially proportional to the free run rotational speed are detected and the rotational direction is detected from the phase of each of two axial voltage components, variational period of ripple sign is slow in low speed regions and a long time is required for surely grasping it, and to provide a device for quickly detecting r.p.m. and the rotational direction, with high precision. <P>SOLUTION: From a current flowing through an induction motor when a command value is applied from a voltage command output unit, the signal of frequency component lower than the frequency component dependent on the circuit time constant of the induction motor is extracted and then the rotational condition is detected from that signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
