| 摘要 |
PROBLEM TO BE SOLVED: To protect a power element being employed in an inverter, or the like, against a voltage induced in a motor by delivering an operation stop command if the highest set revolutional speed for low speed winding is exceeded when a winding switching command has been switched to the low speed winding side. SOLUTION: A three-phase synchronous motor 6 is fixed with an encoder 7 and the output from the encoder is delivered through a speed detecting section 8 to a winding switching command section 13 for switching a winding switch 5. Outputs from the speed detecting section 8 and the winding switching command section 13 are inputted to an operation decision section 14. In case of low speed winding operation determined based on a command from the command section 13 and an output from the detecting section 8, the operation decision section 14 delivers a switching command to high speed winding when the revolution speed of the motor exceeds the highest set value for low speed winding and stops operation of an inverter 4 after a switching is made to high speed winding through the winding switch 5. According to the arrangement, a power element 15 in the inverter 4 can be protected by stopping operation of the inverter 4 at a point sufficiently lower than the maximum rated voltage level of the power element 15. |
