| 摘要 |
PURPOSE: To speedily detect reduction in capacitance of a smoothing capacitor when an electric induction motor to hoist an elevator is driven by an inverter. CONSTITUTION: A DC voltage detecting circuit 17 detects DC voltage smoothed by a smoothing capacitor 3, and sends it out to a control circuit 5. The control circuit 5 judges that capacitance of the smoothing capacitor 3 is reduced when ripple voltage contained in the DC voltage becomes large. |
