| 摘要 |
<P>PROBLEM TO BE SOLVED: To detect any open phase in three-phase power supply without fail by an inexpensive method that does not call for any dedicated circuit. <P>SOLUTION: An open phase detector includes a rectification unit 2 that rectifies the three-phase alternating-current power supply 1 into direct-current voltage, a smoothing unit 3 that smooths the direct-current voltage rectified at the rectification unit, an inverter 4 that uses the smoothed direct-current voltage as power supply, a three-phase motor 5 driven by the inverter, a frequency detecting means 6 that detects the pulsating flow cycle of the smoothed direct-current voltage, and a control unit 7 that computes the pulsating flow cycle of the voltage detected by the frequency detecting means. When the pulsating flow cycle of direct-current voltage detected by the control unit 7 within a predetermined time after start of the three-phase motor 5 is equal to or lower than a predetermined value, the control unit 7 determines that an open phase has occurred and transmits a stop signal to the inverter 4 to stop the three-phase motor 5. Thus, when an open phase occurs, that is quickly and reliably detected to protect the inverter 4. Such troubles as damage are thereby prevented from occurring in a controller due to operation in open phase state. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
