| 摘要 |
PURPOSE:To automatically release the DC controlling functions when a motor is driven below the comercial speed by a method wherein, when the voltage between both terminals of a smoothing capacitor has reached the fixed value or above, the specific arm only of an inverter is conducted and a DC current is applied to an AC motor. CONSTITUTION:When the motor 5 is decelerated to an N2 speed from a revolution speed N1 at the point t0 using a speed setting device 9, the output frequency of the inverter 4 is changed from F1 to F2 for a soft circuit 10. As a result, the voltage between the terminals of the smoothing capacitor 3 increases from V0 by having regenerative braking, and when said voltage has reached Vx, a signal is applied only to the specific arm of the inverter 4 from a distributor 13 by the signal outputted from an overvoltage detecting device 16 and the revolution speed of the motor 5 is suddenly reduced in the section between t1 and t2 by having DC braking. When the number of revolution has been reduced to the value corresponding to the output of the soft circuit 10, the overcurrent deteting device 16 discontinues to output signals and the motor 5 receives regenerative braking in the sections between t2 and t3. The above-mentioned procedures are repeatedly performed. |
