| 摘要 |
PURPOSE:To suppress the rise of a DC voltage in an inverter even if the load of an induction motor to be driven by operating frequency rising means when the fact that the load of the motor is abruptly reduced is detected by load detecting means, and temporarily rising the output frequency of control means. CONSTITUTION:When a relay 11 is deenergized, an electric contact 9 is closed, an electric contact 10 is opened, and a contact 12 is simultaneously opened. As a result, a solenoid valve 6 is opened, a solenoid valve 7 is closed, hydraulic pressure operated from a hydraulic pump 8 to a hydraulic driver 5 is released, and a brake shoe 4 is separated from a brake drum 3. In this case, a 3-phase induction motor 2 abruptly becomes a no load state. This state is transmitted to an inverter 1 through the contact 12. The inverter 1 which receives a signal from the contact 12 temporarily slightly rises its oscillation frequency. Thus, the inverter 1 does not become a regenerative mode, and the rise of its DC voltage is suppressed. |
